1. Field of the Invention
The present invention relates to a method for determining molding characteristic and an injection molding machine which facilitates identifying a problem when a molding trouble occurs during molding by the injection molding machine.
2. Description of the Prior Art
When a trouble such as defective molding occurs during injection molding by an injection molding machine, it is impossible to determine whether the trouble is caused by the molding machine, resin or a mold, which requires examination of its cause one by one. In a case where a problem resides in the molding machine, especially in a check valve, a degree of friction is measured by taking out a screw.
The resins of the same kind have different resin properties between their lots or by differences of drying temperature, time for being left or mixing ratio of regenerant, which requires the examination of the resin properties. Conventionally, the resin properties are examined using a special measuring apparatus.
In the case where neither the molding machine nor the resin has the problem, then the mold is examined for finding the cause of the molding trouble.
As described above, when trouble such as the defective molding occurs, it is impossible to determine whether the trouble is caused by the molding machine, resin or mold, so that the examinations of the cause have to be carried out at random, which takes time to solve the problem.
The present invention has its object to provide a method for determining molding characteristic and an injection molding machine which can determine, when a trouble occurs in the injection molding machine, whether the trouble is caused by a molding machine, resin or a mold.
In order to achieve the above object, the present invention injects resin with a nozzle in an injection molding machine left open to detect an injection pressure produced at that time by a pressure sensor, stores a pressure data detected by the pressure sensor as reference pressure data together with the screw position data or the lapse of time in storing means, and obtains a detected pressure data with respect to the screw position or time when the resin having a different condition such as difference of resin lots, difference of drying temperature, difference of mixing ratio of regenerant or difference of time for being left is injected with the nozzle left open under the same molding condition as that used in an injection with the nozzle left open. Variation of molding characteristic is determined by displaying the detected pressure data and the reference pressure data stored in the storing means on displaying means.
Further, resin is injected with a nozzle left open under each molding condition in compliance with scheduled molding condition to obtain reference pressure data under each molding data to be stored in storing means, and the resin having a different condition is injected with the nozzle left open under a certain or an optional molding condition in obtaining the reference pressure data to obtain detected pressure data and to determine variation of molding characteristic by displaying the reference pressure data having the same molding condition as that used in obtaining the detected pressure data and the detected pressure data on displaying means. If reference pressure data includes no data having the same molding condition, the reference pressure data with respect to the corresponding molding condition is found by interpolating from each reference pressure data stored in the storing means to be displayed.
Moreover, with respect to resin having a different condition, each detected pressure data is obtained under the same scheduled molding condition as in obtaining the reference pressure data to display the detected pressure data and the reference pressure data stored in the storing means correspondingly to the molding condition on the displaying means to determine variation of the molding characteristic.
The molding condition scheduled includes at least conditions of temperatures of a nozzle and a cylinder and a condition of injection speed. Data such as the molding condition in obtaining the data, date, kind of the resin are simultaneously stored when the reference pressure data is detected to be stored.
A controller of the injection molding machine is connected to the personal computer by communication means, the reference pressure data is stored in the storing means provided on the personal computer, and the reference pressure data and detected pressure data are input in the personal computer to be displayed on said displaying means. In this case, data such as a code for identifying the molding machine, the molding condition in obtaining the data, date, kind of the resin are simultaneously stored together with the reference pressure data.
In order to automatically determine the molding characteristic described above, an injection molding machine is provided with a pressure sensor for detecting an injection pressure; storing means for injecting resin with a nozzle in an injection molding machine left open to store a pressure detected by said pressure sensor as reference pressure data together with the screw position data or the lapse of time; and comparing means for outputting an alarm when detected pressure data with respect to the screw position and time obtained by injecting the resin having a different condition with said nozzle left open under the same molding condition as that used in an injection with said nozzle left open exceeds setting monitoring width of said reference pressure data.